Recent years have seen the rapid development of displays based on liquid crystal display systems, cathode ray tube (CRT) display systems, organic electroluminescent display systems, and laser-based display systems. A portion of the display system development efforts appear to be directed to large area displays and, more particularly, to large area flat-panel displays. For example, in a publication by A. Abileah and Z. Yaniv, titled "Optical Tiled AMLCD for Very Large Display Applications", SPIE, Vol. 1664, High Resolution Displays and Projection Systems, pp 241-243, 1992, there is described a method of tiling a number of flat-panel liquid crystal displays (LCDs) to a continuous large display using magnifying fiber optic faceplates to cover the gaps between adjacent displays. R. Samadani, J. Lanham, D. Loomis, L. Silverstein, and J. Larimer, in a publication titled "Periodic Plane Tilings: Application to Pixel Layout Simulations for Color Flat-Panel Displays," Journal of the SID, Vol. 2/2, pp 95-104, 1994 discuss algorithms for pixel tilings and at minimizing a potentially objectionable observation of individual pixels in a display of pixels. U.S. Pat. No. 5,015,999 discloses a display unit for displaying two-dimensional images in which a two-dimensional array of organic electroluminescent elements emits ultraviolet light which is directed to a fluorescent screen having fluorescent materials emitting different colors of visible light. In a PCT International Patent Application No. WO 94/18802, there are disclosed methods and apparatus for image projection using linear laser arrays, with each laser array generating multiple parallel output beamlets at one of the three primary colors (red, green, and blue), combining the beamlets of the three colors into a plurality of white light beamlets which are then raster scanned in an optical scanning and projection system to be projected onto a screen. U.S. Pat. No. 5,424,771 discloses a video display device using laser generated radiation, in which respective red, green, and blue laser beams are combined and raster scanned by a rotating polygon and rotating lenses for projection onto a wall or a large, white surface. And U.S. Pat. No. 5,473,396 discloses a display apparatus in which ultraviolet emitting CRTs emit radiation representing red, green, and blue image information and projecting these UV emissions onto a large size fluorescent screen having a pattern of fluorescent materials which emit visible red, green, and blue light upon excitation by the UV rays from the CRTs.
While LCDs, in general, can be considered as flat-panel displays, their utility in providing very large area displays is restricted to the LCD used as a light valve in projection. Thus, an LCD light valve display is a display having a long projection distance and is, therefore, not a flat-panel projection display. CRT-based display devices become impractical for large display screen sizes and can not generally be considered in applications as flat-panel display systems due to the physical dimensions of cathode ray tubes. Display systems based on organic electroluminescent light emitting elements can be viewed as flat-panel displays, however, the display screen size or display screen area is limited by the size or area of available substrates for forming the organic electroluminescent elements.
Display systems utilizing laser light sources offer the principal advantages of high brightness and optical coherence of a laser beam over a distance sufficient to afford manipulation of the beam by beam deflection elements and beam scanning elements so as to make possible laser beam projection onto a display screen of a relatively large display screen area. In particular, the advent of semiconductor lasers (also referred to as laser diodes) has offered the possibility for display system designers to advance more compact laser-based display systems than was possible when more bulky gas laser sources were used.
In order to provide on a display screen a two-dimensional representation of information, a laser beam or laser beams, suitably intensity modulated, are projected onto the screen in a raster pattern which is generated in the form of horizontal laser beam scanlines which are advanced vertically along the display screen as a sequence of parallel scanlines. These horizontal scanlines are produced by sweeping a laser beam or laser beams across the display screen through reflection of the beams off the surfaces of multifaceted rotating polygonal mirrors. Each successive horizontal scanline is displaced vertically from a previous horizontal scanline by a second reflector which is also known as a galvanometer reflector. While the operational reliability of rotating multifaceted polygonal mirrors has been improved, such laser beam steering systems are complex and expensive. Moreover, particulate contamination or haze formation of one or several mirror facets would adversely affect the performance of such rotating laser beam deflectors. Accordingly, it is desirable to provide horizontal laser beam deflection or horizontal laser beam scanline formation by a non-rotating deflector element.
Currently known laser-based color projection systems deploy a fixed number of laser light sources, for example, a linear array of red light emitting, green light emitting, and blue light emitting laser sources, respectively. In such projection display systems, the viewable display area on a screen can, in principle, be increased from one area to a larger area by increasing the distance between the laser beam projection source and the screen. Stated differently, currently known laser projection display systems provide a fixed information content on a display screen, irrespective of the area covered by the display. Accordingly, it is desirable to provide a laser-based scaleable flat-panel color projection display in which both the number of laser light sources illuminating a display screen, and the display area of the screen can be readily scaled so as to meet user needs for projection displays which extend from relatively small area flat-panel color displays to relatively large area flat-panel color displays.
Presently known color projection display systems use a plurality of laser light sources dedicated to provide a plurality of primary color laser beams, followed by elements dedicated to combining these differently colored laser beams prior to a beam scanning or a beam rastering assembly. Thus, such systems require optically refractive and optically reflective elements capable of performing designated functions over a broad spectral range extending from red light to blue light. In order to achieve a comparable optical efficiency throughout that relatively broad spectral range, optical elements tend to require a more complex design which, in turn, increases the cost of such elements. Accordingly, it is desirable to provide a flat-panel projection display which uses a plurality of laser scanners each generating a raster-scanned laser light beam of one and a same wavelength, and generating a full-color display on a patterned fluorescent full-color display screen by projecting the raster-scanned laser light beams thereon.